Vibro Compaction

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Vibro Compaction
Vibro Compaction, also known as VibroflotationTM,
is used to densify clean, cohesionless soils. The
action of the vibrator, usually accompanied by
water jetting, reduces the inter-granular forces
between the soil particles, allowing them to move
into a denser configuration, typically achieving
a relative density of 70 to 85 percent.
Compaction is achieved above and below the water
table.
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Vibro CompactionProcess
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Vibro CompactionProfile of Sand Grains
Volume reduction due to densification of
non-cohesive soils may result in surface
settlement of 5 to 15 of the treated depth.
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Vibro Compaction Design Considerations

• The design approach for Vibro technologies will
  generally be governed by one or more of the three
  major categories of site improvement
• Shear resistance increase
• Settlement control
• Liquefaction lateral spreading mitigation

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Vibro CompactionRange of Treatable Soils
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Vibro Compaction Design Requirements

• Design of the Vibro program requires information
  on
• Total loads (structure, surcharge, live, wind and
  seismic)
• Soil type (variation, stratigraphy, groundwater
  location)
• Type of footing/slab design
• Structural settlement tolerance
• Site restrictions and limitations
• To address the above issues, the Vibro program is
  designed such that the zone of influence of the
  vibratory probe ensures the necessary soil
  densification and/or reinforcement.

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Vibro CompactionDensification Results
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Vibro CompactionExpected Results
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Vibro Compaction Design Steps

• 1. Perform site investigation
• Soil gradation important
• 2. Calculate performance with existing soil
  conditions
• Problem understood
• 3. Establish compaction requirements
• Sufficient densification to reduce settlement
  and/or prevent liquefaction
• 4. Develop appropriate Vibro Compaction approach
• Treat entire site or just footing?
• 5. Establish testing criteria
• Relative density, SPT, CPT, PMT, etc.

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Vibro Compaction Increased Bearing Capacity

• Bearing capacity is a function of the soils
  shear strength which is derived from the soils
  angle of internal friction (f) and/or cohesion
  (c). The Vibro systems increase the allowable
  bearing capacity by increasing the effective f
  angle.
• Vibro Compaction densifies cohesionless granular
  soils, thus increasing the angle of internal
  friction directly. The allowable bearing capacity
  is calculated with conventional procedures using
  the improved angle.

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Vibro Compaction Reduced Settlement

• Settlement is a function of the soils modulus
  and consolidation character. Vibro systems
  decrease the settlement that will occur beneath a
  proposed foundation by either directly increasing
  the in situ soils modulus value and/or by
  constructing high modulus Vibro stone columns in
  a grid pattern beneath the planned foundation.
• Vibro Compaction densifies cohesionless granular
  soils, thus increasing the soils modulus value
  directly. The settlement is calculated with
  conventional procedures using the improved
  modulus value.

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Vibro Compaction Quality Control

• Compaction point locations
• Resistance level as measured by amp meter
  (vibrator draws
• more current in denser soils)
• Quantity of fill added or reduction in site level

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Vibro Compaction Acceptance Testing

• Standard Penetration Test (SPT)
• Cone Penetrometer Test (CPT)
• Pressuremeter Test (PMT)
• Dilatometer Test (DMT)
• Load test

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Vibro CompactionBenefits

• Increases bearing capacity and reduces foundation
  size
• Reduces foundation settlement
• Mitigates liquefaction potential
• Permits construction on granular fills

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Vibro Replacement Stone Columns extends the range
of soils that can be improved by vibratory
techniques to include cohesive soils.
Densification and/or reinforcement of the soil
with compacted granular columns or stone
columns is accomplished.
Vibro ReplacementStone Columns
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Vibro ReplacementStone Columns

• Cohesive, mixed and layered soils generally do
  not densify easily when subjected to vibration
  alone. The Vibro Replacement Stone Columns
  technique was developed specifically for these
  soils, effectively extending the range of soil
  types that can be improved with the deep
  vibratory process.
• With Vibro Replacement Stone Columns, columns of
  dense, crushed stone are designed to increase
  bearing capacity, reduce settlement, aid
  densification and mitigate the potential for
  liquefaction, and improve shear resistance.

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Vibro ReplacementStone Column Process
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Vibro ReplacementStone Column Construction

• The two primary methods of Vibro Stone Column
  construction are
• Wet, Top Feed Method (Replacement and
  Displacement)
• In this technique, jetting water is used to
  remove soft material, stabilize the probe hole,
  and ensure that the stone backfill reaches the
  tip of the vibrator. This is the most commonly
  used and most cost-efficient of the deep
  vibratory methods. However, handling of the spoil
  generated by the process may make this method
  more difficult to use on confined sites or in
  environmentally sensitive areas.

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Vibro ReplacementTop-Feed Construction Method
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Vibro Replacement

• Dry, Bottom Feed Method (Displacement)
• This technique uses the same vibrator probes as
  standard Vibro Replacement Stone Columns, but
  with the addition of a hopper and supply tube to
  feed the stone backfill directly to the tip of
  the vibrator. Bottom Feed Vibro Replacement is a
  completely dry operation where the vibrator
  remains in the ground during the construction
  process. The elimination of flushing water in
  turn eliminates the generation of spoil,
  extending the range of sites that can be treated.
  Treatment is possible up to a depth of 80 feet
  and is not inhibited by the presence of
  groundwater.

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Vibro ReplacementBottom-Feed Construction Method
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Vibro Replacement Design Steps

• 1. Perform site investigation
• Soil type, gradation, consolidation, and
  strength important
• 2. Calculate predicted improvement
• Problem understood
• 3. Establish requirements of ground improvement
• What settlements, factor of safety, etc., are
  allowable
• 4. Design Vibro Replacement scheme
• Number of stone columns and/or performance
  requirements required to achieve desired results
• 5. Establish testing criteria
• Load test, SPT, area of stone columns

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Vibro Replacement Important Parameters

• Ground conditions
• Relative density
• Degree of saturation
• Permeation

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Vibro ReplacementDesign Considerations

• The design approach for Vibro technologies will
  generally be governed by one or more of the three
  major categories of site improvement
• Shear resistance increase
• Settlement control
• Liquefaction lateral spreading mitigation

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Vibro ReplacementDesign Considerations
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Vibro ReplacementDesign Requirements

• Design of the Vibro program requires information
  on
• Total loads (structure, surcharge, live, wind and
  seismic)
• Soil type (variation, stratigraphy, groundwater
  location)
• Type of footing/slab design
• Structural settlement tolerance
• Site restrictions and limitations
• To address the above issues, the Vibro program is
  designed such
• that the zone of influence of the vibratory probe
  ensures the
• necessary soil densification and/or reinforcement.

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Vibro CompactionDensification Results
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Vibro ReplacementExpected Results
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Vibro Replacement Increased Bearing Capacity
Vibro Replacement constructs dense, Vibro stone
columns in the zone requiring improvement. The
allowable bearing capacity can be calculated by a
variety of methods, such as the one developed by
Priebe in The Design of Vibro Replacement,
Ground Engineering, December 1995. If any of the
in situ soils are granular, their improved value
should also be accounted for in the design.
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Vibro Replacement Reduced Settlement

• Vibro Replacement constructs high modulus dense
  Vibro stone columns in the zone requiring
  improvement. The anticipated settlement can be
  evaluated by a variety of methods, such as the
  Priebe method.
• This method provides an improvement factor based
  on the stone columns angle of internal friction
  and the percentage of the treatment zone replaced
  by stone (area replacement ratio).
• In addition, if any of the in situ soils are
  granular, their improved parameters should also
  be included in the design.

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Vibro ReplacementReduced Settlement
Method to estimate settlement reduction using
stone columns in cohesive soils
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Vibro ReplacementLiquefaction Prevention

• Seismic motion causes pore pressure to increase.
  When the pore pressure increases to equal
  interstitial grain-to-grain stresses,
  liquefaction is initiated. The soil then loses
  shear strength, resulting in bearing failures and
  slope instability, followed by large deformations
  (horizontal and vertical)
• Site improvement by densification has proven to
  be the most effective solution. Densification
  will increase interstitial stresses, thus
  preventing liquefaction and settlement
• Densification is required to preclude excessive
  settlements and offers the most secure remedy to
  multiple ground accelerations (aftershocks)

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Vibro ReplacementEmbankment Subgrade Improvement

• Vibro stone columns increase the slope stability
  safety factor especially when they attract
  sufficient loading to increase shearing
  resistance. The shear strength of treated soil
  depends on the shear strength of the untreated
  soil, the transverse shear strength of the
  columns, the area replacement ratio and the load
  conditions.

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Vibro ReplacementTypical Arrangement of Stone
Columns
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Vibro Replacement Quality Control

• Production Monitoring
• Quantity and quality of backfill added
• Vibrator amperage draw
• Treatment depth
• Post-Construction Testing
• Standard Penetration Testing (SPT)
• Cone Penetrometer Testing (CPT)
• Dilatometer Testing (DMT)
• Load Testing
• Shear Wave Velocity Profiling

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Vibro Replacement Benefits

• Permits shallow footing construction
• Reduces foundation settlement
• Increases bearing capacity, allowing reduction in
  footing size
• Mitigates liquefaction potential
• Prevents earthquake-induced lateral spreading
• Provides slope stabilization
• Permits construction on fills

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Dynamic Compaction
Weights of 10 to 30 tons Drop heights of 50 to
100 ft Impact grids of 7 x 7 ft to 20 x 20 ft
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Dynamic Compaction
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Dynamic Compaction
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Dynamic Compaction
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